Alignment of nucleotide sequences and translation of IG heavy chain CDR3. DNA extracted from lung explant specimens was amplified using the FR1/JH BIOMED-2 PCR protocol. After purification, PCR fragments were directly sequenced. (A) Sequences were aligned to immunoglobulin sequences using IMGT/V-QUEST¹⁸  and IMGT/JunctionAnalysis,¹⁹  from IMGT, the international ImMunoGeneTics information system (http://imgt.cines.fr). Somatic mutations were defined as nucleotide substitutions after elimination of the known polymorphisms described in the IMGT database.²⁰  (B) The same database determines the ability of sequences to code for functional heavy chains. First line includes amino acid positions according to the IMGT unique numbering for V-DOMAIN.²¹